This invention relates to a novel peptide mimetic compound having potent in vivo activity as an inhibitor of platelet aggregation.
Fibrinogen is a glycoprotein present as a normal component of blood plasma. It participates in platelet aggregation and fibrin formation in the blood clotting mechanism.
Platelets are cellular elements found in whole blood which also participate in blood coagulation. Fibrinogen binding to platelets is important to normal platelet function in the blood coagulation mechanism. When a blood vessel receives an injury, the platelets binding to fibrinogen will initiate aggregation and form a thrombus. Interaction of fibrinogen with platelets occurs through a membrane glycoprotein complex, known as gpIIb/IIIa; this is an important feature of the platelet function. Inhibitors of this interaction are useful in modulating platelet thrombus formation.
It is also known that another large glycoprotein named fibronectin, which is a major extracellular matrix protein, interacts with fibrinogen and fibrin, and with other structural molecules such as actin, collagen and proteoglycans. Various relatively large polypeptide fragments in the cell-binding domain of fibronectin have been found to have cell-attachment activity. See U.S. Pat. Nos. 4,517,686; 4,589,881; and 4,661,111. These polypeptides include an internal amino acid sequence Arg-Gly-Asp-Ser (RGDS). Certain relatively short peptide fragments from the same molecule were found to promote cell attachment to a substrate when immobilized on the substrate or to inhibit attachment when in solubilized or suspended form. See U.S. Pat. Nos. 4 578,079 and 4,614,517. These peptides were defined as EQU X-Arg-Gly-Asp-R-Y
wherein
X=H or amino acid, PA1 R=Thr or Cys; and EQU X-Arg-Gly-Asp-Ser-Y PA1 X=H or amino acid, PA1 Y=OH or amino acid. PA1 Directly inhibits the binding of .sup.125 I-fibrinogen to thrombin activated human platelets. PA1 Inhibits aggregation of human and dog platelets in vitro to a variety of proaggregatory stimuli: Thrombin, collagen, ADP. PA1 Induces a sustained antiplatelet effect during constant intravenous infusion. PA1 Possesses a relatively short duration of action permitting rapid termination of antiplatelet effects if required by the clinical situation. PA1 Exhibits no effects on human neutrophil elastase release or degranulation. PA1 Lacks acute hemodynamic or electrocardiographic effects in dogs at infusion rates that are 10 times higher than those required to achieve 90% inhibition of platelet aggregation in this species. PA1 Lacks CNS effects in mice at 0.5, 1, 2, and 24 hours following a dose of compound that was 20-fold greater than the rat antiplatelet ED.sub.50.
wherein
In U.S. Pat. No. 4,683,291, inhibition of platelet function is disclosed with synthetic peptides designed to be high affinity antagonists of fibrinogen binding to platelets. These synthetic peptides have up to 16 amino acid residues with EQU Arg-Gly-Asp-Val or EQU Arg-Gly-Asp-Ser
at the C-terminal.
Similar synthetic peptides which contain the Arg-Gly-Asp sequence and their use as inhibitors of fibrinogen binding to platelets are disclosed by Koczewiak et al., Biochem. 23, 1767-1774 (1984); Plow et al., Proc. Natl. Acad. Sci. 82, 8057-8061 (1985); Ruggeri et al., Ibid. 83, 5708-5712 (1986); Ginsberg et al., J. Biol. Chem. 260 (7), 3931-3936 (1985); Haverstick et al., Blood 66 (4), 946-952 (1985); and Ruoslahti and Pierschbacher, Science 238, 491-497 (1987). Still other such inhibitory peptides are disclosed in EP patent application Nos. 275,748 and 298,820.
In U.S. Pat. No. 4,857,508, certain novel tetrapeptide derivatives are disclosed which have enhanced activity as inhibitors of platelet aggregation. These tetrapeptide derivatives contain the sequence X-Gly-Asp-Y in which X and Y are defined to comprise a variety of organic moieties. An illustrative preferred example is Arg-Gly-Asp-(O-methyl-Tyr)-NH.sub.2.